An access point may be configured to communicate with a variety of stations. These stations may include mobile terminals, such as cellular telephones, personal digital assistants (PDAs) or the like, as well as sensors that are configured to provide information regarding various sensed parameters. As association may be established between an access point and a station, such as the result of the exchange of a plurality of signals. As long as relatively frequent communication occurs between the access point and the station, the association between the access point and a station may be maintained and need not be reestablished, thereby avoiding the overhead associated with the exchange of signals required to establish the association. However, a station, such as a sensor, may sometimes communicate with the access point on a repeated, but an infrequent basis with substantial periods of silence there between.
A maximum idle period may be defined to indicate the maximum period of time for which an access point will maintain the association with a station in the absence of any communication therebetween. In order to conserve energy, the station may enter a sleep mode during periods in which the station does not communicate with the access point. Thus, a station may potentially sleep for a period of time equal in duration to the maximum idle period without being disassociated from the access point. The establishment of a maximum idle period therefore allows the station to save energy with idle periods having longer durations allowing longer periods of sleep without the requirement to disassociate from the access point, while also allowing resource management by the access point.
The access point may provide the stations with an information element that defines the maximum idle period. As shown in FIG. 1, one example of an information element that may be provided by the access point to the station in order to define the maximum idle period is illustrated. As shown, this information element may include an element identifier field, a length field, a maximum idle period field and an idle options field. In one example, the element identifier field, the length field and the idle option field are each one octet in length, while the maximum idle period field is two octets in length. As such, the maximum idle period of this example may be a sixteen bit unsigned integer. In an instance in which the value 0 of the maximum idle period field is reserved and the time period is specified in units of 1,000 time units (TUs), the maximum idle period can have a maximum length of 216−1=65,535 seconds since a 1,000 TUs is approximately equal to one second. Stated differently, the maximum idle period may have a maximum length of approximately 1,092.25 minutes or 18.2 hours. In this example, a station that desires to remain associated with an access point beyond 18.2 hours would be required to transmit a message, such as a keep alive message, to the access point, thereby interrupting the sleep mode of the station and requiring otherwise unnecessary transmissions between the station and the access point. However, a failure to transmit a keep alive message or to otherwise communicate with the access point within the maximum period of 18.2 hours of this example would result in the access point and the station being disassociated, thereby requiring the overhead associated with the re-association messages that must be communicated between the access point and the station at a later time in order to reestablish the association.
In some instances, the maximum idle period as described in the foregoing example may not be sufficiently long. As such, it has been proposed in an article entitled “Consideration on Max Idle Period Extension for 802.11ah Power Save”, doc IEEE 11-12/69r2 that the time period of the maximum idle period field be specified in units of about 10 seconds instead of units of about 1 second, thereby allowing a station to remain associated with an access point for about 182 hours or approximately 7.5 days. By simply increasing the size of the units in which the time period defined by the maximum idle period field is specified, the granularity of the maximum idle period becomes more coarse so as to limit the specificity with which a station may be disassociated from an access point. Additionally, this uniform increase in the length of the maximum idle period, while appropriate for some stations, may cause other stations to be associated with an access point for a longer period of time than is actually required, thereby unnecessarily consuming resources, such as the memory, of the access point. Further, even a maximum idle period of about 7.5 days may be insufficient in some instances depending upon the frequency with which a station communicates with an access point, such as the frequency with which a sensor reports data to an access point.